1. Field of the Invention
This invention relates to passenger vehicle loading ramps having a pivotally mounted cab or vestibule on its outer movable end, and more particularly to an improved mounting means for supporting a vestibule on the outer end of such ramps for pivotal movement throughout a wide angle to accommodate conveyance vehicles disposed at a wide range of angles relative to the longitudinal axis of the ramp.
2. Description of the Prior Art
Conveyance loading ramps of the type employed to provide an enclosed passageway bridging the space between a terminal building and a conveyance vehicle are commonly made up of a plurality of telescoping tunnel sections which are relatively movable to extend and retract the ramp as necessary to position the open end of the passageway adjacent an open door in a conveyance vehicle which may be located at various distances from and at different orientations relative to the terminal building. Such loading ramps are most commonly employed in connection with the loading and unloading of passengers onto and from airplanes and the invention will be described herein with respect to such apparatus, it being understood that the invention could also be employed in connection with ramps used with other conveyance vehicles.
Known aircraft loading ramps normally have one end pivotally mounted on a fixed support at the terminal building and the other end supported on an undercarriage, sometimes referred to as a buggy, having wheels which are driven to extend and retract the ramp steered to enable driving the outer end of the ramp to and from a loading position adjacent an aircraft door. However, since the ramps are employed to load and unload various types of aircraft, and since the aircraft are not always parked on the same bearing or at the same location on the apron, it is generally necessary to make special provisions for engaging the airplane at an angle enabling the open end of the tunnel bridge to form a generally weathertight seal with the airplane around the door opening. This is accomplished by providing means for raising and lowering the outer, movable end of the bridge and by providing an aircraft vestibule mounted on such outer end for limited horizontal swinging movement about a vertical axis to enable the open end of the vestibule to squarely engage the sides of the airplane around the door opening regardless of the angular relationship, within limits, of the longitudinal axis of the tunnel bridge with respect to the plane of the door.
When the ramp is inclined from the terminal to the aircraft so that the floor of the vestibule is not level, a tripping hazard is created at the aircraft door when the aircraft is positioned and oriented on the apron so that the vestibule must be rotated substantially from a straightline continuation of the ramp, as is described in U.S. Pat. No. 3,561,030 assigned to the assignee of the present invention. In that patent, the ramp is provided on its outer end with an enlarged articulated head which is mounted for limited pivotal movement about a transverse horizontal axis to maintain the floor horizontal at the outer end of the ramp, the vestibule is mounted for pivotal movement on this articulated head so that the vestibule floor remains level and the tripping hazard is avoided regardless of the orientation of the vestibule about its pivotal axis. However, mounting the horizontally swingable vestibule on the vertically pivotable articulated head has presented difficulties, and generally has required an excessively heavy, strong vestibule structure.
Movable vestibules of this type must be of sufficient size to completely encompass an aircraft door to provide freedom of movement of passengers therethrough. Also, movement of the loading ramp is normally controlled from an operator's booth on one side of the vestibule so that the operator has a clear view through a transparent windshield to enable the operator to swing the vestibule into position and to drive the movable end of the ramp into the desired loading position with respect to an aircraft door. Thus, the vestibules are necessarily both relatively large and heavy which, in combination with the live load to be carried, has presented problems in mounting the vestibule for such swinging movement.
In the past, it has generally been the practice to mount the movable vestibule on the outer end of a loading ramp by use of a combination of a fixed pivot support with a roller and track support located one at the top and the other at the bottom portion of the vestibule. For example, U.S. Pat. No. 3,412,412 discloses a loading ramp in which the top of the vestibule is pivotally supported by an elongated arm having one end rigidly mounted to the top wall of the movable vestibule and its other end pivotally supported on the fixed top wall of the outer end portion of the tunnel. The bottom portion of the vestibule is provided with a plurality of pairs of support rollers with each pair including a horizontally mounted roller engaging a first track to provide vertical support and a vertically mounted roller engaging a second track to provide lateral support. Such support requires that substantial loads be transferred through the sidewall structure of the vestibule so that relatively rigid, load bearing walls are required. The reverse of the general arrangement disclosed in U.S. Pat. No. 3,412,412 is also known, i.e., an arrangement whereby the bottom wall and frame structure is supported for rotation about a vertical pivot spaced rearward from the outer end of the ramp and the top wall and frame structure is supported by rollers engaging arcuate tracks, with the result again being that substantial loads must be transferred through the vestibule sidewall structure.
U.S. Pat. No. 3,315,291, assigned to the assignee of the present application, discloses a horizontally swingable vestibule structure including a relatively large structural platform assembly projecting rearwardly therefrom and supporting a substantial segment of the floor of the adjacent end portion of the passenger tunnel. The platform is pivoted for swinging movement about a vertical pivot shaft located near its centroid. This rearwardly projecting, generally arcuate portion of the platform overlies a portion of the frame of the tunnel and is supported by rollers engaging upwardly and downwardly directed surfaces to provide stability to the structure. Such an arrangement, however, does not readily lend itself to use in combination with an articulated head on the outer end of the ramp for maintaining the floor of the ramp horizontal at the area adjacent the aircraft door.